The present invention relates to an improved spinneret for use in producing composite filaments, particularly the so-called "islands-in-a-sea" type synthetic composite filaments or "core-in-sheath" type synthetic composite filaments.
The term "islands-in-a-sea" type composite filaments used herein refers to filaments, whereby each mono-filament consists of at least two synthetic polymeric filamentary constituents incorporated into a filament body, with a plurality of filamentary island constituents being substantially embedded in a filamentary seal constituent. The island constituents are independent from each other and extend axially over the length of the filament. In view of the cross-sectional profile of the "islands-in-a-sea" type, the island consituents are located as a plurality of islands in the sea consituent, which appears as a sea, and this profile is substantially retained throughout the length of the composite filament.
The term "core-in-sheath" type composite filaments used herein refers to filaments, whereby each mono-filament consists of a synthetic polymeric filamentary constituent with another kind of filamentary constituent being substantially embedded in the former constituent. Such a filament may be referred to as a "primary composite filament". The above mentioned "islands in a sea" type filament may be referred to as a "secondary composite filament".
It is well known that such an "islands-in-a-sea" type composite filament is used to form a bundle of filaments having a very fine denier, which consists of only the island constituents when the sea constituent is removed from the composite filament. In this respect, such composite filaments are well known as material, in the form of filaments or staples, to be used in valuable non-woven fabrics, woven fabrics or knit goods.
In connection with this, it has been noted that attaining a higher density of the island constituents distributed in the sea constituent implies that a lesser amount of the sea constituent is to be removed from the composite filament, and, thus, becomes economically very advantageous. Further, in a case of the composite filaments having a considerable high density of the island constituent relative to the sea constituent, such filaments are, in practice, advantageous for the reason that they are available as finish filaments, without being subjected to the sea removing process. This is because in this case they can exhibit adequetely inherent characteristics of the island constituents through the thin covering sea constituent.
In this respect, many attempts of spinning "islands-in-a sea" type composite filaments having a high density of the island constituents have been made recently. In these attempts, it has been noted that, as the proportion of the sea constituent is reduced, production of desirable composite filaments rely on how the island constituents are distributed uniformly, in a cross-sectional view, in the sea constituent by using a spinneret. However, in the case of a composite filament having a considerably large proportion of the island constituents relative to the sea constituent, particularly in an extreme case where the sea constituent is reduced to be of the minimum proportion necessary to separate the island constituents from each other so that most of the cross-sectional of the composite filament is occupied by the island constituents, it is very difficult to produce, with assurance, such composite filaments for a long period of time by using the spinneret, while maintaining a uniform distribution of the island constituents in the sea constituent. In this case, according to the prior art, the following difficulties have been encountered. For example, referring to FIG. 1 shown in an axial cross-sectional view of a conventional spinneret, the spinneret has inlet holes 8 through which primary composite streams, of a simple core-in-sheath form, each consisting of a stream of a sea constituent polymer melt A and a stream of an island constituent polymer melt B embedded therein, are produced. The spinneret has uniting chambers 9, in which the primary composite streams are united to form secondary composite streams, and has extruding outlets or orifices 10 connected to the respective uniting chambers, through which the secondary composite streams are extruded.
According to the spinneret as shown in FIG. 1, while spinning composite filaments for a long period of time, it was noted that many cases occurred, in practice, wherein the island constituent streams, to be separated from each other in the united sea constituent stream, were partially fused with each other and/or the island constituents streams were exposed or disclosed partially from the circular surfaces of the secondary composite streams or the resultant filaments. In extreme cases, the resultant filaments had sections having a cross-sectional profile consisting almost entirely of either the sea constituent A or the island constituent B.
Such defective phenomena were likely to occur as the ratio of the island constituent B to the sea constituent A was increased.
Under the circumstances, the inventors investigated the defective phenomena and have found that they result from the unstable flow of the core-in-sheath type streams, that is, of the primary composite streams. Referring to FIG. 1, the defective phenomena occur due to a difference in the flow rates between the sea constituent melts A, which flow from a combining chamber 5 to the extruding outlets 10a and 10b through the corresponding uniting chambers 9, which outlets 10a and 10b are positioned in an outer circumferential zone and an inner circumferential zone, respectively, in a cross-sectional view.
This is because it is considered that the sea constituent melts A travel for different periods of time with different thermal hysteresis, until they are extruded from the outlets 10a and 10b, respectively, with the result that the apparent viscosities of the melts become different from each other.
In the above processes of the sea constituent melts A, the sea constituents streams become incompletely united, in a cross sectional view, and also have different diameters, in a cross-sectional view, and, thus, as time lapses, there may occur cases where a part of the sea constituent melt A is replaced by the island constituent, in a cross-sectional view, and in an extreme case it may occur that only the island constituent B occupies the entire cross-sectional area, that is, the longitudinal sections of the secondary composite stream are occupied by the island constituent B.